Rev 08/30/2023
Ophidascaris robertsi (Sprent & Mines, 1960), Sprent, 1988
Synonym:
Amplicaecum robertsi Sprent & Mines, 1960
See genus description and Sprent, 1963a,b
Intestinal parasites of carpet pythons (Morelia spilota) in Australia
Carpet pythons (Morelia spilota) in Australia.
The carpet python is a large species of Morelia, between 2 and 4 m long and weighing up to 15 kg . Males are typically smaller than females; in some regions, females are up to four times longer than males.
Adult nematodes inhabit the esophagus and stomach of the definitive host (carpet python). Eggs are passed in the snake's feces and are ingested by various small mammals which serve as intermediate hosts.
In the intermediate host, larvae migrate to thoracic and abdominal organs where, particularly in marsupials, the third-stage larvae may reach lengths of 7-8cm.
The cycle is completed when pythons consume infected intermediate hosts (Hossain et al., 2023).
In experimental infection, laboratory-reared carpet snakes: infected with embryonated eggs resulted in second-stage larvae in the tissues which did not develop further.
Infection with third-stage larvae, resulted in two distinct migratory patterns depending upon the maturity of the larvae administered. Larvae from the liver of laboratory rats which had been infected less than 12 weeks previously, migrated to various tissues, especially the aorta, of the snake, where they remained coiled in cysts filled with clotted blood for periods up to 112 days. Growth occurred within the cysts, but moulting did not occiur, In contrast, larvae from the liver of laboratory rats infected 12 weeks or more previously, and from mice infected for 8 weeks or more, underwent the third moult in the wall of the oesophagus and stomach of the snake.
With the onset of the fourth stage, the development of the reproductive organs was evident and continued during the fourth stage. Fourth-stage larvae may remain encapsulated in the wall of the stomach or oesophagus until sex differentiation is completed, after which the fourth moult occurs and the adult parasite emerges, leaving two sheaths of the same length within the capsule (Sprent, 1963a).
Second-stage larvae have a wide range of hosts, including earthworms, snails, fish, tadpoles, reptiles, birds, and mammals. Development to the third-stage was only observed to occur in birds and mammals. Second-stage larvae in the tissues of invertebrates and lower vertebrates could be transferred by feeding to reptiles, birds and mammals. Development proceeded in these hosts to the same extent as occurred following egg infection.
Third-stage larvae could be transferred to certain snakes and lizards by feeding liver of infected rodents, but third-stage larvae over 3 mm. could not be transferred to mammals. Third-stage larvae were found to be uninfective at all stages of growth for birds. Besides the carpet snake, the third and fourth moult was observed to occur in the goanna (Varanus spp.), the blue-tongued lizard (Tiliqua scincoides) and the bearded dragon (Amphibolurus barbatus). No growth in length was observed and no eggs were evident. As far as is known, none of these lizards is a definitive host of O. robertsi (Sprent, 1963b).
Ecophysiological Parameters:
Humans would be considered accidental hosts of Ophidascaris robersti. In 2021, a 64-year-old woman from New South Wales, Australia, was admitted to a local hospital after 3 weeks of abdominal pain and diarrhea, followed by dry cough and night sweats. Subsequently, in 2022, she was experinecing forgetfulness and worsening depression. Brain magnetic resonance imaging (MRI) revealed a right frontal lobe lesion. In a biopsy, a live third-stage larval specimen of Ophidascaris robertsi (8cm long, 1mm diam.) was removerd from the frontal lobe lesion (Hossain et al., 2023).
The woman resided in an area where she often collected native vegetation, warrigal greens (Tetragonia tetragonioides), from around a lake to use in cooking. Hossain et al. (2023) hypothesized that she inadvertently consumed eggs of O. robertsi either directly from the greens or indirectly by contamination of her hands or kitchen utensils.
Hossain, M.E., Kennedy, K.J., Wilson, H.L., Spratt, D., Koehler, A., Gasser, R.B., Slapeta, J., Hawkins, C.A., Bandi, H.P., Senanayake, S.N. 2023. Human Neural Larva Migrans Caused by Ophidascaris robertsi Ascarid. Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 29, No. 9: 1900-1903.
Sprent J.F.A. 1963a. The life history and development of Amplicaecum robertsi, an ascaridoid nematode of the carpet python (Morelia spilotes variegatus). I. Morphology and functional significance of larval stages. Parasitology. 153:7-38). https://doi.org/10.1017/S0031182000072498
Sprent J.F.A. 1963b. The life history and development of Amplicaecum robertsi, an ascaridoid nematode of the carpet python (Morelia spilotes variegatus). II. Growth and host specificity of larval stages in relation to the food chain. Parasitology. 53:321-327. https://doi.org/10.1017/S0031182000072796
Sprent. J.F.A. 1988. Ascaridoid nematodes of amphibians and reptiles: Ophidascaris Baylis, 1920. Systematic Parasitology 11: 165-213.